Conventionally, a method is provided in which moving image data in which a telop portion of the moving image is encoded is directly extracted without decoding. This method includes a step of judging whether the encoded moving image data is a frame that is encoded using a correlation between frames or a frame that is encoded without using correlation between frames; a step of determining, for the frame that is encoded using a correlation between frames, whether a pixel therein is encoded without applying motion compensation; a step of storing an encoded value in a two-dimensional counting matrix corresponding to the position of the pixel; a step of comparing the value stored in each counting matrix with a threshold value; and a step of identifying a pixel having a value determined to be larger than the threshold value as the telop portion. Such an operation is executed to each pixel in a predetermined area, and the telop of the moving image can be extracted by reviewing the operations (see, for example, Patent Document 1 below).
A telop region detecting apparatus has been proposed that can detect appearance of a telop at a high speed and with high precision and can extract the position of the telop in a frame from compressed-encoded data itself or from information formed by encoding only a portion thereof. In the telop region detecting apparatus, only necessary information is decoded partially from the encoded data by a variable length decoding unit and the decoded information is delivered to a time change judging unit, a telop position judging unit, and an appearing frame judging unit. The time change judging unit sets in I picture a region that is a candidate telop region. The telop position judging unit picks up a block having an encoding mode suitable for the telop from the I picture. The appearing frame judging unit executes a frame judging process that judges from which frame the telop appears (see, for example, Patent Document 2 below).
Patent Document 1: Japanese Patent Application Laid-Open Publication No. H9-322173
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2002-64748